refactor: remove /users/{uid}/settings/{setting} route

@baris Also, I am now allowing the following properties to be saved in User.saveSettings:
- categoryTopicSort
- topicPostSort
- setCategorySort
- setTopicSort

public/openapi/write/users/uid/settings/setting.yaml

@@ -1,40 +0,0 @@
-put:
-  tags:
-    - users
-  summary: update one user setting
-  parameters:
-    - in: path
-      name: uid
-      schema:
-        type: integer
-      required: true
-      description: uid of the user
-      example: '1'
-    - in: path
-      name: setting
-      schema:
-        type: string
-      required: true
-      description: name of the setting you wish to update
-      example: 'showemail'
-  requestBody:
-    content:
-      application/json:
-        schema:
-          type: object
-          properties:
-            value:
-              type: string
-              example: '1'
-  responses:
-    '200':
-      description: successfully updated user settings
-      content:
-        application/json:
-          schema:
-            type: object
-            properties:
-              status:
-                $ref: ../../../../components/schemas/Status.yaml#/Status
-              response:
-                type: object